Figure 16.8 Predicting the outcome of competition for a single resource. Based on the Lotka-Volterra competition equations, there are four possible outcomes of competition. (a) If the zero population growth isocline for species 1 is farther out than species 2, species 1 will increase to its carrying capacity and species 2 will go extinct. (b) If the isocline for species 2 is farther out than species 1, species 2 will increase to its carrying capacity and species 1 will go extinct. (c) If the isoclines cross and the two carrying capacities are the outermost points on the two axes, the winner depends on the initial number of each species. (d) If the isoclines cross and the two carrying capacities are the innermost points on the two axes, then the two species will coexist. As in Figure 16.7, the green line represents the population isocline for species 1 and the purple line represents the population isocline for species 2. The thin black arrows represent increases and decreases in population sizes for each species whereas the thick black arrows represent the net effects of population changes in both species.